In packet switching networks, it is frequently important to effect end-to-end packet flow control so that a high data throughput rate is achieved without overloading the network. In one flow control scheme known as end-to-end windowing, the packets of a data stream are numbered sequentially. A window, described by left and right edges, restricts the sequence numbers of packets that the sender may transmit at any given instant. The receiver responds to received packets with positive acknowledgements which cause the sender's window to move ahead.
In the windowing scheme described in an article by D. Belnes, "Flow Control in the Packet Switching Networks," Communications Networks, Uxbridge, England, pages 349-361, 1975, the sender establishes the window size. The sender begins transmitting packets into the network at a high rate and sets the window size equal to the number of packets outstanding at the instant the first positive acknowledgement is received. In effect, what is done is that the sender makes an instantaneous measurement of round-trip delay and adjusts the window accordingly. Although it is possible to make frequent adjustments in the window size as the round-trip delay varies, for example, due to network congestion, such adjustments represent processing overhead. It is therefore desirable in many applications to set the window once as a packet connection is being established and then leave the window unchanged for the duration of the connection. In such applications, the Belnes scheme is undesirable since a larger window size is set if the connection happens to be established at a time when the network is unusually congested such that the measured round-trip delay is long. While a large window increases throughput, it operates to further aggravate the congestion by allowing a larger number of packets to be in transit through the network.
In view of the foregoing, a recognized problem in the art is the unsuitability of end-to-end windowing arrangements where the sender determines the window size based on instantaneous network delay characteristics.